If it's a quality pot, it shouldn't be crunchy or have noise. It's a passive item, so that should eliminate the possibility of weird induced noises, alternator whines, loops, etc.
Simple unit, really; Note that this will trim the entire signal from whatever RCA you use with it. This is different from a remote gain control in that it will attenuate to 0 or restore to full whatever voltage is coming from the RCA; likely the headunit outs, whereas a gain control leaves the original signal intact, and adjusts it at the amplifier end.